1) ONE WHO CAUSES MERIT FOR OTHERS WILL NOT SIN
QUESTION: The Gemara says that "Kol ha'Mezakeh Es ha'Rabim, Ein Chet Ba Al Yado" -- no sin will come upon the hands of a person who causes merit for other people [by teaching them Torah]. The Gemara reasons that it is not proper for the teacher to be in Gehinom while the students are in Gan Eden.
However, the Gemara elsewhere mentions that it is possible for a person to teach Torah to others and still be a sinner. The Gemara in Chagigah (15b) relates the story of "Acher" (Elisha ben Avuyah) who taught Torah (even the great Rebbi Meir was his student) and yet became a notorious sinner. Similarly, the Gemara in Yevamos (109b) says that if a person thinks that even though he sins he is still entitled to reward because he taught Torah to others who then went and fulfilled Mitzvos, he is incorrect. How is the Gemara in Chagigah and Yevamos, which imply that a person who teaches Torah to others has no guarantee that he will not sin, to be reconciled with the Gemara here which says that one who causes merit for others will not sin? (TOSFOS YESHANIM)
(a) TOSFOS in Yevamos (109b, DH Mahu) and the TOSFOS YESHANIM here answer that the guarantee that no harm will befall a teacher of Torah applies only to one who never sinned prior to teaching. The merit of causing others to fulfill Mitzvos stands in his stead to prevent him from sin. The case of Acher and the Gemara in Yevamos refer to people who were sinners before they started to teach Torah. (As the Gemara in Chagigah says, heretical books fell from Acher's lap as a youngster when he arose from the Beis Midrash, and he frequently hummed gentile tunes.)
(b) RAV YECHEZKEL ABRAMSKY zt'l in CHAZON YECHEZKEL (Tosefta Yoma 4:11) explains that the Gemara here does not refer to one who teaches Torah to others merely to help them increase their knowledge. Rather, it refers to one who teaches Torah in order to "purify their minds and thoughts through Torah. This, in turn, distances them from sin as they immerse themselves in Torah and Mitzvos." Rav Abramsky interprets the word "Mezakeh" not to mean "Zikuy" (merit), but to mean "Zikuch" (purification). Acher taught only the facts from the Torah; he did not help his students internalize what they had learned and develop into greater people through Torah. Likewise, the Gemara in Yevamos refers to a person who teaches the laws to his students but does not teach them how to become G-d-fearing individuals. (Rav S. Yudaikin, in DIVREI SHALOM 5:6, expands on this theme. See there (5:7) for another answer based on the BEN YEHOYADA.)
2) STANDING FOR AN ELDER WHO IS BEING CARRIED
QUESTION: The Gemara says that when Rav Zutra would be carried into the Beis Midrash on the Shabbos before a Yom Tov (for the public lecture prior to the Yom Tov), he would avoid any feelings of haughtiness by saying to himself the verse, "For strength is not everlasting, and does the crown [of glory] last from generation to generation?" (Mishlei 27:24). RASHI (DH Mekatfi Lei) explains that since he was old, his students would carry him on their arms outstretched on each other's shoulders. In this manner, the people would not have to inconvenience themselves to stand up for him in the Beis Midrash.
Rashi's words are not clear. First, Rashi initially states that the reason they carried him was because he was old (and presumably unable to walk on his own). Rashi then says that he was carried so that the people would not have to inconvenience themselves to stand for him.
Second, why are the people exempt from standing for someone who is carried?
ANSWER: RASHI elsewhere (Beitzah 25b and Sanhedrin 7b) explains in more detail the practice of carrying a sage into the Beis Midrash. Since the sage was old, it would take him a long time to get to his seat in the Beis Midrash. The people there would have to stand for a long time as he slowly made his way to his seat. His attendants would carry him so that he would reach his seat sooner and the people would not have to stand for so long.
This explains why Rashi first says that they carried Rav Zutra because he was old, and then he says that they carried him so that the people would not have to stand up for him. They carried him because he was old and walked slowly, and had he walked to his place the people would have had to remain standing.